1. Field of the Invention
The present invention relates to a method and an apparatus for printing, capable of performing maintenance operations, while printing a plurality of images on a continuous sheet, at intermediate areas located between one of the images and next one of the images.
2. Description of the Related Art
In an inkjet printing apparatus, in the case where printing is performed using a rolled continuous sheet used for mass printing such as laboratory printing, maintenance operations for maintaining the performance of equipment used in the printing apparatus are sometimes performed while the continuous sheet is being conveyed. As to a maintenance operation requiring printing on a surface of the continuous sheet in such maintenance operations, a required maintenance pattern is printed on a non-image part that is an intermediate area located between areas where images being products are to be printed and that is an area where image printing is not intended.
Each of the maintenance patterns has the purpose of maintaining the performance of equipment and there exists a plurality of patterns such as, for example, a preliminary ejection pattern, a misfiring monitor pattern, a register adjustment pattern, a position adjustment pattern. The preliminary ejection pattern is printed for the purpose of stabilizing ink ejection by preventing a nozzle from being clogged during printing and periodically performing preliminary ejection at intervals causing no defective ink ejection, in the inkjet printing apparatus. The misfiring monitor pattern is printed for the purpose of periodically monitoring whether defective ink ejection occurs due to misfiring of ink from a nozzle during printing. The register adjustment pattern is printed for the purpose of periodically correcting a timing lag (hereinafter, also referred to as misregistration) of ink ejection onto the sheet surface which would occur from moment to moment during printing. Each maintenance pattern is controlled to be printed on a non-image part located between one image and next image in accordance with a mutually different purpose and with different frequency for each maintenance operation.
In Japanese Patent Laid-Open No. 2011-240492, control is performed so as to print, in a predetermined order, a plurality of maintenance patterns including the preliminary ejection pattern and the misfiring monitor pattern and unit images. In addition, even in the case where a joint of the rolled continuous sheet has been detected, control is performed so as to change the order of printing the respective maintenance patterns such that the respective maintenance patterns are printed at fixed intervals.
In the maintenance patterns, there exist ones required to be analyzed by a reader. In the case of the above-mentioned misfiring monitor pattern, the pattern formed on the sheet surface is read by the reader and analysis is performed so as to clarify the presence or absence of misfiring nozzle by nozzle. The pattern to be read is required to have a high resolution corresponding to an arrangement resolution of nozzle arrays a print head includes, and analysis is performed, for each print, on all the nozzles used for printing. Therefore, in the case of the misfiring monitor pattern, the amount of computation of data processing is large. Furthermore, the resister adjustment pattern is also one of the maintenance patterns analysis of which is necessary, and after the pattern has been formed, the pattern is read by the reader and analysis is performed in the same manner as the misfiring monitor pattern. The pattern to be read is required to have a resolution which is high enough to allow recognition of dot displacement of ink droplets. In addition, since there exist many factors which would constitute a contributing factor for misregistration, the amount of computation which is required to derive a plurality of amounts of misregistration to be corrected for the contributing factor is also large. Therefore, in the case of the register adjustment pattern, the amount of computation of data processing becomes further larger than that of the misfiring monitor pattern. In this manner, the amount of data processing is enormous both for the misfiring monitor pattern and the register adjustment pattern. Although the time required for analysis greatly depends on the performance of a CPU, even a high-grade CPU cannot reduce, to zero, the processing time of a large amount of data, which is required at the time of analyzing the maintenance pattern. Accordingly, a certain period of time is required for analysis although the analysis depends on the processing capability of the CPU mounted on the reader.
Here, control of printing a plurality of maintenance patterns simply in predetermined order will be considered.
In controlling to print the plurality of maintenance patterns in the predetermined order, it is assumed that the misfiring monitor pattern and the register adjustment pattern may be sometimes printed at neighboring positions on the sheet surface. In this case, the register adjustment pattern is read after the misfiring monitor pattern has been read and while it is being analyzed. That is, analysis of the misfiring monitor pattern is temporarily suspended, the register adjustment pattern is read, and thereafter analysis of the misfiring monitor pattern is restarted. As to the misfiring monitor pattern, analysis processing is temporarily suspended because of interruption of reading of the register adjustment pattern. As to the register adjustment pattern, after the pattern has been read, analysis is to be started, waiting until analysis of the misfiring monitor pattern is terminated. Therefore, it takes more time for printing the misfiring monitor pattern and the register adjustment pattern than it originally takes for analyzing each of the misfiring monitor pattern and the register adjustment pattern. At the time of falling into such a case, a timing at which a printing apparatus recognizes discovery of misfiring of a nozzle is delayed in the case of the misfiring monitor pattern and thus misfiring of the nozzle is left as it is, which leads to useless printing of images that are unworthy for the products. In addition, in the case of the register adjustment pattern, since the actual amount of misregistration varies with time, a difference between a past misregistration amount derived from analysis and a current misregistration amount is increased. Therefore, in the case where correction is performed on the basis of that analysis, degradation of image quality may possibly be induced let alone improvement of image quality. As mentioned above, in the case where the maintenance patterns, analysis of which is required, interfere with each other, there arise problems in which maintenance operations cannot be performed in real time, thereby leading to the increase in amount of useless printed materials and the degradation of image quality of the printed materials as a result.
In addition, a non-image part (also referred to as a non-image area or a blank area as the case may be) which includes the maintenance pattern is an area to be separated from the image being the product and to be finally discarded as a waste. In contrast to this, the discardable waste size of the non-image part is determined in advance for reasons of configuration of the printing apparatus. In controlling of printing the plurality of maintenance patterns in predetermined order, a case where many maintenance patterns are printed on one non-image part is also assumed. At this time, in the case where the size of the non-image part is not within the discardable size for reasons of configuration of the printing apparatus, there will be increased the possibility that paper jam occurs in the printing apparatus due to contact of the continuous sheet on a conveyance path with a paper waste that is left not-discarded. In the case where paper jam actually occurs, a large amount of time is taken for recovery of the printing apparatus including post-processing of the paper jam. In addition, a product, printing of which has been in progress, is wasted, thereby leading to a large disadvantage including the fact that ink and the continuous sheet are uselessly consumed.
In the method for printing maintenance patterns in Japanese Patent Laid-Open No. 2011-240492, in changing the printing order, the influence caused by mutual interference of the maintenance patterns is not taken into account. Therefore, Japanese Patent Laid-Open No. 2011-240492 cannot solve the above-mentioned various subject matters.